Microstructure and mechanical properties of WC-(Ti,W)C-Co hardmetals fabricated by in-situ carbothermal reduction of oxides and subsequent liquid phase sintering

Abstract

WC-(Ti,W)C-Co hardmetal was fabricated using carbon black, WC, Co, WO3, TiO2 as raw materials, through an energy-efficient and cost-efficient method that the process of carbothermal reduction of oxides and the liquid phase sintering of hardmetal were combined in one heating cycle. Phase transformation and microstructure characteristics of the hardmetals were examined by XRD, SEM, EDX, and TEM. Moreover, mechanical properties were tested with related mechanical property testing instruments. Results demonstrated that the in-situ carbothermal reactions and outgassing processes had finished below 1200 ℃. Microstructures of hardmetal consisted of WC grains, (Ti,W)C solid solution, and Co binder phase. Moreover, the mean size of WC and (Ti,W)C grains were both smaller than those of hardmetal prepared with TiC powders. A coherent relationship between Co and (Ti,W)C grain was noticed. Moreover, a coherent relationship between two (Ti,W)C grains was observed. Compared with hardmetal prepared with TiC powders, TRS and KIC were improved. The increase of TRS was chiefly due to the smaller grain size and the coherent interface structure. Moreover, the increase of KIC was ascribed to the (Ti,W)C solid solution and the coherent interface structure. Hardmetals prepared through this method showed good mechanical properties with a hardness of 90.7 ± 0.2 HRA, a TRS of 3007 ± 87 MPa, a KIC of 13.1 ± 0.2 MPa·m1/2.